Check valves are very common in various applications for controlling the flow of gaseous or liquid fluids in the above described manner. With regard to the operation of the valves between their fully or partly open and closed conditions, such check valves are normally of one of three major types. Specifically, the check valves may be operated between their different positions by a control means acting directly or indirectly upon a valve member for regulating the flow through the valve. This type of valve also includes manual operation of the control means or the valve member. It is mostly used in pneumatic and hydraulic fluid systems requiring a relatively sophisticated control of the fluid flow, for providing a regulated flow in one direction and/or a fluid tight seal against flow in the other direction. This type of valve is therefore comparatively expensive and not suitable for use in applications requiring only a simple inexpensive device for preventing back-flow.
A second major type of check valve is provided with a separate biasing means, normally in the shape of a spring, constantly urging the valve/valve member(-s) towards the closed condition. In other words, the valve member or members is/are maintained in the open position by the flowing fluid, against the biasing force, and is/are automatically closed once the fluid flow stops. This type of valve is normally only operated between a fully open and a fully closed condition. Since the biasing force has to be overcome by the flowing fluid, a relatively large pressure drop is created across the valve. This general type of valve is disclosed i.a. in U.S. Pat. No. 6,011,689, where a cooling system for a computer has redundant cooling air fans employing back-flow preventing vents having hinged vanes that are pivotal about vertical axes. In order to secure closing of the respective vent in the event that the associated fan fails, each of the pivotal vanes are provided with a spring urging the vane towards the closed position. The vanes are caused to pivot to the open position by the fan airflow, overcoming the biasing force. Thereby, the vanes offer considerable resistance to said airflow and cause a pressure drop across the back-flow preventing valve.
The third major type of check valve is similar to the second type, the main difference being that the valve has no separate biasing means. Instead, the force of gravity is employed for automatically urging the valve/valve member(-s) to the closed condition in the absence of fluid flow. This type of valve normally comprises a number of parallel vanes or louvers that are pivotal about a horizontal axis. The vanes are normally arranged so that adjacent vanes partly overlap each other in the closed position. With such a configuration, the pressure drop across the valve will still be noticeable since the force of gravity has to be overcome by the fluid flow. Attempts have been made to reduce the resulting pressure drop by lowering the weight of the individual vanes or alternatively by designing the vanes so that they provide less resistance to the airflow. Even with such attempts, the blades still cause a pressure drop that may be unacceptable in certain applications. Lowering the weight of the blades may also cause vibration and resulting noise and a special design for the blades will inevitably lead to an increased cost for manufacturing the valves. Examples of such valves are disclosed in i.a. U.S. Pat. Nos. 6,181,557B1 and 6,000,623.
The two latter types of “check valves” have lately been frequently used in applications relating to the cooling of electronic equipment. In such applications, not least within the telecommunication field, where electronic equipment is normally provided in an enclosure, such as a cabinet, the heat generated by the equipment has to be removed in an efficient manner in order to maintain proper operation of the equipment. This is accomplished by employing one or several fans configured to have a capacity for providing an adequate cooling airflow. In order to secure such an adequate airflow at all times it has become common practice to provide cooling systems employing parallel redundant fans. In other words, at least one backup-fan is provided to secure adequate temporary cooling even in the event that one fan fails. In such applications, it is highly desirable to employ a one way valve for each fan, normally provided immediately at the fan outlet, so that back-flow through a disabled fan may be prevented. Such back-flow may otherwise jeopardize the effect of the entire cooling system for the equipment. The above mentioned Patents are all specifically directed to valves for such applications.
U.S. Pat. No. 6,042,348 discloses a variant of a back-flow preventing valve for use in a forced air cooling system for electronic equipment. Said valve is provided with vertically arranged pivotal vanes. The vanes are not intended to close under the force of gravity or by any external means but entirely by the pressure differential that will be caused by the failure of the associated fan. In order to secure prompt closing of the valve in case of fan failure, such a design requires that in their fully open position the vanes form a relatively large angle with the direction of flow through the valve. Otherwise, the existing differential pressure may not be sufficient to securely close the valve. Therefore, the vanes will also in this case inevitably cause an undesirable pressure drop across the valve.
The above discussed pressure drop caused by the back flow preventing valve may be critical in many applications, such as in cabinets accommodating electronic equipment, where said pressure drop may have the effect that more powerful fans are required in order to provide adequate cooling. In many instances, the cabinets are of a standard size and the restricted space within the cabinets does not permit that the fans are upgraded in capacity.
Accordingly, there is a need within this art for a redundant fan cooling system having reliable valve means associated with each of the fans for preventing back-flow of air through the disabled fan and offering a very small resistance to the cooling air flowing through the valve in the open position thereof.